Plastic integrated circuit package and method and lead frame for making the package

ABSTRACT

Packages for an integrated circuit die and methods and leadframes for making such packages are disclosed. The package includes a die, a die pad, peripheral metal contacts,.bond wires, and an encapsulant. The die pad and contacts are located at a lower surface of the package. The die pad and the contacts have side surfaces which include reentrant portions and asperities to engage the encapsulant.  
     A method of making a package includes providing a metal leadframe having a die pad in a rectangular frame. Tabs extend from the frame toward the die pad. The die pad and tabs have side surfaces with reentrant portions and asperities. A die is attached to the die pad. The die is electrically connected to the tabs. An encapsulant is applied to the upper and side surfaces of the leadframe. Finally, the leadframe is cut in situ so that the die pad and tabs are severed from the frame, the sides of the package are formed, and the package is severed from the leadframe.

FIELD OF THE INVENTION

[0001] The present invention is to directed toward an improved plasticpackage for an integrated circuit die, and a method of making such apackage.

BACKGROUND OF THE INVENTION

[0002] Integrated circuit die are conventionally enclosed in plasticpackages that provide protection from hostile environments and enableelectrical interconnection between the integrated circuit die andprinted circuit boards. The elements of such a package include a metalleadframe, an integrated circuit die, bonding material to attach theintegrated circuit die to the leadframe, bond wires which electricallyconnect pads on the integrated circuit die to individual leads of theleadframe, and a hard plastic encapsulant material which covers theother components and forms the exterior of the package.

[0003] The leadframe is the central supporting structure of such apackage. A portion of the leadframe is internal to the package, i.e.,completely surrounded by the plastic encapsulant. Portions of the leadsof the leadframe extend eternally from the package and are used toconnect the package externally.

[0004] Further background information concerning conventional plasticintegrated circuit packages and leadframes is contained in chapter 8 ofthe book Microelectronics Packaging Handbook (1989), which was edited byR. Tummala and E. Rymaszewski, and is published by Van NostrandReinhold, 115 Fifth Avenue, New York, N.Y.

[0005] A problem with conventional plastic packages is that theirinternal leadframes limit reduction of the size of the packages.Practitioners have attempted to reduce the size of packages byeliminating internal leadframes, as is shown in U.S. Pat. No. 4,530,152to Roche et al and U.S. Pat. No. 5,172,214 to Castro, but these packageshave numerous disadvantages. The contacts of the package shown by Rochein the '152 patent have orthogonal side surfaces. Accordingly, thepackages are believed to be unreliable because the contacts could easilybe pulled from the encapsulant material. The package shown by Castro inthe '214 patent has leads which extend into the body of the package froma lower external surface of the package to the top of the die. Theseleads are large, and have complex bends. Including such leads in apackage would increase manufacturing costs and limit reductions in thelateral size of the package. By contrast, the contacts of the packageswithin the present invention are simpler, do not have such bends, andallow for packages of smaller lateral size.

SUMMARY OF THE INVENTION

[0006] The present invention is to directed toward improved plasticpackages for housing an integrated circuit die, and to leadframes andmethods for making such packages. The packages of the present inventionare easier and less expensive to make than conventional plasticpackages, and are more reliable and efficiently-sized than conventionalpackages.

[0007] In one embodiment of an assembly method for a package within thepresent invention, Step 1 provides a metal leadframe. The leadframeincludes a rectangular frame, e.g., a square frame. A substantiallyplanar die pad is within and connected to the frame. A plurality offinger-like rectangular tabs extend from the frame toward the die padwithout contacting the die pad. The number and location of the tabsaround the frame may vary. The die pad and the tabs have peripheral sidesurfaces which include a reentrant portion(s) and asperities. Thereentrant position(s) and asperities enhance the connection of the diepad and tabs to the plastic encapsulating material.

[0008] Step 2 places and attaches an integrated circuit to a firstsurface of the die pad.

[0009] Step 3 electrically connects a bond wire or an equivalentconductor between each bonding pad of the die and a first surface of oneof the tabs.

[0010] Step 4 places the leadframe on a flat surface, with the diefacing upwards, and applies a viscous encapsulant material onto theupward facing first surface of the leadframe. The encapsulant materialis then hardened. The encapsulant material covers the die, the bondwires, a first surface of the tabs, the first surface of the die pad,the side surfaces of the die pad and tabs, and all or part of the framesaround the die pad. A lower second surface of the leadframe, including alower second surface of the die pad and tabs, is not covered withencapsulant.

[0011] Step 5 plates the exposed surfaces of the leadframe, includingthe exposed second surfaces of the die pad and tabs with a metal, suchas copper, gold, lead-tin solder, tin, nickel, palladium, or anysolderable metal.

[0012] Step 6 cuts the encapsulated portions of the leadframe with asaw. In particular, step 6 either obliterates the disposable portions ofthe leadframe, or severs the disposable portions of the leadframe fromother components of the leadframe, such as the die pad and tabs, whichare to be included in the package. Step 6 also trims the encapsulantmaterial and thereby forms the peripheral sides of the package.

[0013] A feature the packages built by the above described method isthat the die pad and contacts (i.e., the severed tabs of the leadframe)of the package are located at the lower first surface of the package.The first surfaces and side surfaces of the die pad and tabs areinternal to the package, i.e., covered with encapsulant material, butthe second surfaces of the die pad and tabs are not covered byencapsulant material. The die pad and tabs are isolated from each otherby encapsulant material.

[0014] In a completed package, only the encapsulant material holds thedie pad and contacts to the package. The connection of the encapsulantmaterial to the die pad and contacts is enhanced by the reentrantportion(s) and asperities of the side surfaces of the die pad andcontacts. The reentrant portions and asperities of the side surfaces ofthe die pad and contacts function as encapsulant fasteners or leadlocks.

[0015] Numerous variations of the leadframe, package, and assemblymethod described above also are described in this application. In onealternative assembly method, a leadframe is provided which allows aplurality of packages to be constructed simultaneously.

[0016] A leadframe for constructing a plurality of packagessimultaneously includes, for example, a matrix of interconnectedrectangular frames. A die pad is within and connected to each of theinterconnected frames. A set of tabs extend from each frame toward thesides of the enclosed die pad without contacting the die pad. Asubsequent encapsulation step includes applying an encapsulant materialonto the surface of the leadframe to which the dies are attached. Thisstep covers the dies and the side surfaces of the die pads and tabswithin a single block of encapsulant material. The encapsulant materialis then hardened. A cutting step separates individual packages from eachother and from the disposable portions of the leadframe. The cuttingstep also severs the connection between each of the interconnectedframes and the die pad and tabs within each frame.

BRIEF DESCRIPTION OF DRAWINGS

[0017]FIG. 1 is a flow chart of a method of making a package.

[0018]FIG. 2 is a top view of leadframe used for making a package.

[0019]FIG. 3 is an enlarged cross-sectional side view of a circledportion of FIG. 2. FIG. 3 shows an embodiment of a side surface of a diepad and tab.

[0020]FIG. 4 is a first alternative embodiment of a side surface of adie pad and tab.

[0021]FIG. 5 is a second alternative embodiment of a side surface of adie pad and tab.

[0022]FIG. 6 is a third alternative embodiment of a side surface of adie pad and tab.

[0023]FIG. 7 is a top view of the leadframe of FIG. 1 afterencapsulation. The dashed lines are cutting paths for a subsequentsawing step.

[0024]FIG. 8 is a cross-sectional side view of a completed package.

[0025]FIG. 9 is a cross-sectional side view of the package of FIG. 8further including solder interconnection bumps on the package contacts.

[0026]FIG. 10 is a flow chart of a method for making a plurality ofpackages simultaneously.

[0027]FIG. 11 is a top view of a leadframe used for making a pluralityof packages simultaneously.

DETAILED DESCRIPTION

[0028]FIG. 1 shows an exemplary method of assembling a package inaccordance with the present invention. FIG. 8 shows a completed package.

[0029] Step 1 of FIG. 1 provides a metal leadframe. FIG. 2 is a top viewof a first embodiment of a metal leadframe 20 in accordance with thepresent invention. For ease of view, shading is used in FIG. 2 todistinguish the metal portions of leadframe 20 from empty spaces betweenthe-various elements of leadframe 20.

[0030] Leadframe 20 of FIG. 2 is planar or substantially planar and ismade of a conventional leadframe metal, such as copper or copper alloys,plated copper or plated copper alloys, Alloy 42 (42% nickel, 58% iron),or copper plated steel, depending on the application. The opposing upperand lower surfaces of leadframe 20 may be plated with different metals.For example, the tabs 30 and/or other portions of leadframe 20 whichultimately are enclosed within the package may be plated with silver,gold, nickel palladium, or copper. Such plating, for example, mayenhance attachment of bond wires to tabs 30.

[0031]FIG. 2 includes dash lines A--A, B--B, C--C, and D--D. These arelines which indicate where leadframe 20 is cut in Step 6 of FIG. 1. Step6 is described below. FIG. 2 also includes a circle and dashed line 3-3,which indicate the view of FIG. 3.

[0032] Leadframe 20 of FIG. 2 includes a peripheral rectangular frame21. Frame 21 consists of four rectilinear members. The two intersectingpairs of parallel members of frame 21 are denoted as members 22 and 22Aand 23 and 23A. Artisans should understand that the terms “rectangular”or “rectangle” as used herein include a square, which is a rectanglewith four equivalent sides.

[0033] A rectangular die pad 24 is within and connected to frame 21. Diepad 24 has a planar or substantially planar upper first surface 25 and,although it is not shown in FIG. 2, an opposite planar or substantiallyplanar lower second surface 26. Die pad 24 also has peripheral sidesurfaces 27 between upper first surface 26 and lower second surface 26.

[0034] A connector 28 connects two parallel side surfaces 27 of die pad24 to members 22 and 22A of frame 21 of FIG. 2. Each connector 28includes a mushroom-shaped anchor 29, although other shapes may be usedfor anchor 29.

[0035] Three finger-like rectangular tabs 30 are connected to and extendfrom members 23 and 23A toward an adjacent side surface 27 of die pad 24without contacting side surfaces 27. As a result of this configuration,the completed package will have a single row of three contacts on twoparallel sides of the package. Tabs 30 ultimately are severed frommembers 23 and 23A along cut lines C--C and D--D of FIG. 2, and becomethe contacts of the package.

[0036] The number, location, and shape of tabs 30 may vary. For example,instead of having tabs 30 only on members 23 and 23A of frame 21 ofleadframe 20, as in FIG. 2, sets of tabs 30 may be placed on all fourmembers of frame 21. This alternative embodiment would result in theformation of a quad package.

[0037] Each tab 30 of FIG. 2 has a planar or substantially planar upperfirst surface 31 and, although it is not shown in FIG. 2, an oppositeplanar or substantially planar lower second surface 32. Each tab 30 alsohas three peripheral side surfaces 33 between upper first surface 31 andlower second surface 32.

[0038] FIGS. 3-6 show an enlarged cross-sectional side view of thecircled portion of FIG. 2 along line 3-3. In particular, FIGS. 3-6 show,in accordance with the present invention, a side surface 27 of a die pad24 and a side surface 33 of a tab 30 of leadframe 20 of FIG. 2.

[0039] Side surface 27 of die pad 24 and side surface 33 of tab 30 ofFIG. 3 have reentrant portions. In particular, the upper and lowerportions of side surfaces 27 and 33 are reentrant such that there is acentral peak 34 which extends outward from side surfaces 27 and 33 ofdie pad 24 and tab 30, respectively. Encapsulant material flows into thereentrant portions of side surfaces 27 and 33. Central peak 34 extendsinto the encapsulant material.

[0040] The reentrant portions of side surfaces 27 of die pad 24 and sidesurfaces 33 of tabs 30 of FIG. 3 have the function, in a completedpackage, of enhancing the connection between the encapsulating material,on the one hand, and die pad 24 and the contacts of the package (i.e.,severed tabs 30), on the other hand. In addition to having reentrantportions, side surface 27 of die pad 24 and side surface 33 of tab 30 ofFIG. 3 have a roughly-textured surface which includes numerousasperities. Encapsulant material flows into the areas of the asperities.The asperities also enhance the connection between the encapsulantmaterial and die pad 24 and the contacts of the package (i.e., thesevered tabs 30).

[0041]FIG. 4 shows a first alternative profile for side surfaces 27 ofdie pad 24 and side surfaces 33 of tabs 30 of leadframe 20 of FIG. 2. Inthe embodiment of FIG. 4, side surfaces 27 and 33 each have a centraldepression 35 and a roughly-textured surface which includes numerousasperities. Encapsulant material flows into central depression 35 and inthe areas of the asperities. The reentrant portion and asperities ofside surfaces 27 and 33 of FIG. 4 have the function, in a completedpackage, of enhancing the connection between the encapsulant materialand die pad 24 and the contacts of the package (i.e., the severed tabs30).

[0042]FIG. 5 shows a second alternative profile for side surfaces 27 ofdie pad 24 and side surfaces 33 of tabs 30 of leadframe 20 of FIG. 2. Inthe embodiment of FIG. 5, side surfaces 27 and 33 include a rounded lip36 adjacent to upper surface 25 and 31 of die pad 24 and tab 30,respectively. Lip 30 has a roughly-textured surface which includesnumerous asperities. Side surfaces 27 and 33 also have a reentrantorthogonal portion 37 beneath lip 36, adjacent to lower second surface29 and 32 of die pad 24 and tab 30, respectively. Encapsulant materialflows beneath lip 36 and into the area of the asperities. Like theembodiments of FIGS. 3 and 4, the reentrant portions and asperities ofside surface 27 of die pad 24 and side surface 33 of tab 30 of FIG. 5have the function, in a completed package, of enhancing the connectionbetween the encapsulant material and die pad 24 and the contacts of thepackage (i.e., tabs 30 after they are severed from members 23 and 23A).

[0043]FIG. 6 shows a third alternative for side surfaces 27 of die pad24 and side surfaces 33 of tabs 30 of leadframe 20 of FIG. 1. In thisembodiment, side surfaces 27 and 33 each include a rectangular lip 38adjacent to upper surface 25 and 31 of die pad 24 and tab 30,respectively. Side surfaces 27 and 33 also have a reentrant orthogonalportion 39 beneath lip 38 adjacent to lower second surface 29 and 32 ofdie pad 24 and tab 30, respectively. Encapsulant material flows beneathlip 38. Like the embodiments of FIGS. 3-5, the reentrant portions ofside surface 27 of die pad 24 and side surface 33 of tab 30 of FIG. 6have the function, in a completed package, of enhancing the connectionbetween the encapsulant material and die pad 24 and the contacts of thepackage (i.e., severed tabs 30).

[0044] As discussed above, Step 1 of FIG. 1 provides a metal leadframehaving features like those shown in FIG. 2 and either FIGS. 3, 4, 5, or6, or equivalents thereof. Leadframe 20 of FIG. 2 is formed from rolledstrip metal stock by wet chemical etching or mechanical stamping usingprogressive dies.

[0045] As is well known, chemical etching (also known as chemicalmilling) is a process that uses photolithography and metal-dissolvingchemicals to etch a pattern into a metal strip. The photoresist isexposed to ultraviolet light through a photo mask having a desiredpattern, and is subsequently developed and cured. Chemicals are sprayedor otherwise applied to the masked strip, and exposed portions of thestrip are etched away, leaving the desired pattern.

[0046] As is also well known, progressive stamping uses sets ofprogressive dies to mechanically remove metal from a metal strip. Eachof a plurality of stamping stations uses one of the dies to punch adistinct small area of metal from the strip as the strip moves throughthe stations.

[0047] A leadframe 20 having side surfaces like FIG. 3 can be formed bychemically etching the rolled strip metal stock from both sides using aconventional liquid etchant. The etch process is stopped early so thatthere is an underetching of all of the side surfaces of the componentsof leadframe 20, including side surfaces 27 of die pad 24 and sidesurfaces 33 of tabs 30, compared to the time it would take to formvertical side surfaces. The size and shape of central peak 34 of FIG. 2is controlled by the amount of underetching.

[0048] A leadframe 20 having side surfaces like FIG. 4 can be formed bychemically etching the rolled strip metal stock from one side using aconventional liquid etchant. The etch process is continued beyond thetime required to form orthogonal side surfaces for the components ofleadframe 20. The size and shape of central depression 35 of FIG. 3 iscontrolled by the amount of overetching.

[0049] A leadframe 20 having side surfaces like FIG. 5 can be formed ina two step process. The first step of such a process involves forming aleadframe 20 by chemical etching or progressive stamping so that theside surfaces of the components of leadframe 20, including die pad 24and tabs 30, have an orthogonal profile. The second step involvescoining the upper first surface of the leadframe 20, that is, applying ahigh pressure impact to the upper first surface of the leadframe 20.This step deforms the side surfaces of leadframe 40 adjacent to theimpacted surface so that the rounded, asperity-marked protruding lip 36of FIG. 5 is formed.

[0050] A leadframe 20 having side surfaces like FIG. 6 can be formed byprogressive stamping. The side surfaces of the components of leadframe20, including side surfaces 27 of die pad 24 and the side surfaces 33 oftabs 30, can be provided with a rectangular lip 38 and a reentrantorthogonal portion 39 by including intermediate stamping steps which donot fully cut through the rolled strip metal stock before finallycutting through the rolled strip sheet. The intermediate stamping stepsand the final cutting steps combine to form the rectangular, protrudinglips 38 of side surfaces 27 and 33 of FIG. 5.

[0051] Step 2 of FIG. 1 places an integrated circuit die onto upperfirst surface 25 of die pad 24. The placement and attachment of the dieonto die pad 24 may be performed using a conventional die attach machineand conventional die attach adhesives. During Step 2 and the subsequentassembly steps, leadframe 20 of FIG. 2 is grounded to protect againstelectrostatic discharge (“ESD”).

[0052] Step 3 of FIG. 1 electrically connects a conductive metal bondwire between individual bonding pads on the integrated circuit die andthe upper first surface 31 of individual tabs 30 on leadframe 20 of FIG.2. Tabs 30 ultimately become contacts in the completed package, aftertabs 30 are severed from members 23 and 23A of frame 21. Conventionalbond wire attachment equipment may be used for Step 3. Leadframe 20 ofFIG. 2 is grounded during this wiring step to prevent damage to theintegrated circuit dies due to electrostatic discharge. At thecompletion of Step 3, each bonding pad of each die is electricallyconnected to a tab 30 of leadframe 20 of FIG. 1, which is grounded. Tabs30 of leadframe 20 are all shorted together, which facilitates ESDprotection.

[0053] In Step 4 of FIG. 1, the lower second surface of leadframe 20 ofFIG. 2 is placed on a flat surface, and a viscous adhesive encapsulatingmaterial is applied onto the upward-facing upper first surface ofleadframe 20. The encapsulating material is applied so that theencapsulating material covers: the integrated circuit die; the bondwires; any exposed peripheral portions of upper first surface 25 of diepad 24 around the die; side surfaces 27 of die pad 24; upper firstsurface 31 of tabs 30; side surfaces 33 of tabs 33; and part or all ofthe width of members 22, 22A, 23, and 23A of frame 21. The encapsulantmaterial also fills the empty spaces between the components within frame21 of leadframe 20. The encapsulant material does not, however, coverlower second surface 26 of die pad 24 or lower second surfaces 32 oftabs 30 of FIG. 2. In an alternative embodiment, die pad 24 may be upset during the encapsulation step so that a thin layer of encapsulantmaterial forms under lower second surface 26 of die pad 24. If such astep were used, die pad 24 would be completely internal to the package.Finally, the encapsulant material is hardened.

[0054] There are several methods by which Step 4 of FIG. 1 may beaccomplished, depending on the application. For example, as a firststep, leadframe 20 of FIG. 2 is placed on a horizontal surface. As asecond step, a contiguous bead of a conventional hardenable viscousadhesive material, such as HYSOL 4451 epoxy from the Dexter-HysolCompany of City of Industry, Calif., is applied onto the upper firstsurface of side members 22, 22A, 23, and 23A of frame 21 of leadframe 2a of FIG. 2, forming a closed rectangular dam. As a third step, the damis solidified, such as by heating at 150° C. for one hour. As a fourthstep, a conventional hardenable viscous adhesive material suitable forencapsulating packages, such as HYSOL 4450 encapsulant, is appliedwithin the dam so that the incomplete package within the dam is coveredwith encapsulant material. As a final step, the encapsulant material ishardened, such as by heating at 150° C. for one hour, forming a singlesolid block of encapsulant material above and on leadframe 20, includingon its side surfaces.

[0055] Alternatively, Step 4 of FIG. 1 may be accomplished usingconventional plastic molding techniques. In such a method, leadframe 20of FIG. 2 is placed in a mold, and a single block of solid moldedencapsulant material is formed above and on leadframe 20, including onits side surfaces. The encapsulant material may be a conventionalplastic molding compound applied using conventional techniques. Examplemolding compounds include NITTO MP-8000AN molding compound from theNitto Company of Japan, and EME 7351 UT molding compound from theSumitomo Company of Japan. Conventional gates may be formed in leadframe20 to assist in the molding process.

[0056] In Step 5 of FIG. 1, the portions of leadframe 20 of FIG. 2 whichare not covered with the encapsulant material, including lower secondsurface 26 of die pad 24 and lower second surfaces 32 of tabs 30, areplated using a conventional plating metal compatible with printedcircuit boards. For example, exposed second surfaces 26 and 33 of diepad 24 and tabs 30, respectively, may be plated with gold, nickelpalladium, inconel, lead tin solder, or tantalum, depending on theapplication. The plating step is facilitated by the electricalinterconnection of the components of leadframe 20.

[0057]FIG. 7 is a top view of leadframe 20 of FIG. 2 after thecompletion of Steps 1-5 of FIG. 1. A rectangular block of hardenedencapsulant material 40 covers the upper first surface of leadframe 20.Although not shown, encapsulant material 40 also covers side surfaces 27and 33 of die pad 24 and tabs 30, respectively, of leadframe 20. Theblock of encapsulant material 40 in FIG. 7 covers a portion of the widthof members 22, 22A, 23, and 23A of frame 21 of leadframe 20. Theperipheral portions of members 22, 22A, 23, and 23A of frame 21 remainexposed. Alternatively, encapsulant material 40 could be deposited overthe entire upper first surface of leadframe 20. As a second alternative,encapsulant material 40 could be deposited within frame 21 so that tabs30 are covered, but members 22, 22A, 23, and 23A are not covered.

[0058] Step 6 of FIG. 1 cuts leadframe 20 of FIG. 7 in situ. Referringto FIGS. 2 and 7, Step 6 severs the connection between tabs 30 andmembers 23 and 23A of frame 21 of leadframe 20. Step 2 also seversconnectors 28 between die pad 24 and members 22 and 22A of frame 21 ofleadframe 20. Step 6 also cuts encapsulant material 40, forming verticalexternal side surfaces of the package. Finally, Step 6 completes theformation of the package by cutting a completed package away from thedisposable portions of leadframe 20.

[0059] Step 6 may be performed using a saw or other shearing apparatus.To perform Step 6 using a saw, the encapsulated leadframe 20 of FIG. 7is inverted and placed on sticky film. Using the exposed portions ofleadframe 20 as a guide (see FIG. 2), a conventional wafer saw is usedto saw a completed package from the encapsulated leadframe 20.Criss-crossing rectilinear cuts are made along dashed lines A--A, B--B,C--C, and D--D of FIGS. 2 and 7 so that the disposable portions ofleadframe 20, including side members 22, 22A, 23, and 23A of frame 21,connectors 28 and anchors 29, are cut away from the package, isolatedwithin encapsulant material 40, or obliterated by the saw. The cuttingpath of the saw and/or the width of the saw blade should be selected sothat the connections between tabs 30 and members 23 and 23A are severedand side members 22, 22A, 23, and 23A are cut away or obliterated, butall or most of each tab 30 remains intact.

[0060]FIG. 8 is a cross-sectional side view of an exemplary package 50made from leadframe 20 of FIG. 2 according to Steps 1-6 of FIG. 1.Package 50 has a planar or substantially planar external upper firstsurface 51, and an opposite planar or substantially planar externallower second surface 52. Orthogonal external package sides 57 are at theperiphery of package 50 between upper first surface 51 and lower secondsurface 52. Sides 57 were formed during Step 6, when encapsulantmaterial 40 and tabs 30 were cut.

[0061] Lower second surface 52 of package 50 of FIG. 8 consists of diepad 24, a plurality of peripheral contacts 53, and hardened encapsulantmaterial 40. Die pad 24 and each contact 53 are like islands at thelower external second surface 52 of package 50. They are physicallyseparated from each other by encapsulant material 40.

[0062] Die pad 24 and contacts 53 of FIG. 8 are vestiges of leadframe 20of FIG. 2. Referring to FIGS. 2 and 8, contacts 53 of package 50 of FIG.8 were formed when the connections between tabs 30 and members 23 and23A were severed by the saw during Step 6.

[0063] Die pad 24 of FIG. 8 is rectangular and is located at lowersecond surface 52 of package 50. Die pad 24 includes a planar orsubstantially planar upper first surface 25, an opposite planar orsubstantially planar second surface 26, and peripheral side surfaces 27.Second surface 26 of die pad 24 is in the same plane as lower secondsurface 52 of package 50 in FIG. 8, although in alternative embodiments,die pad 24 may be set up into encapsulant material 40.

[0064] Although not fully shown in FIG. 8, rectangular die pad 24 hasfour side surfaces 27 (only two are shown). Each side surface 27 of diepad 24 has a reentrant portion(s), as exemplified by FIGS. 3-6. Inaddition, side surface 27 may have asperities, as exemplified by FIGS.3-5.

[0065] In FIG. 8, integrated circuit die 56 is on and attached to upperfirst surface 25 of die pad 24. Peripheral portions of upper firstsurface 25 are covered by encapsulant material 40. Side surfaces 27 ofdie pad 24 also are covered by encapsulant material 40. Lower secondsurface 26 of die pad 24 is not covered encapsulant material 40, butrather is exposed at lower external surface 52 of package 50. In analternative embodiment (not shown), die pad 24 may be entirely internalto encapsulant material 40 of package 50.

[0066] Two contacts 53 are shown in package 50 of FIG. 8, but sincepackage 50 was constructed from leadframe 20 of FIG. 2, it should beunderstood that package 50 has a set of three contacts 53 on two sides57 of package 50. In alternative embodiments, package 50 could be formedwith a different number or arrangement of contacts, depending on theapplication.

[0067] Each contact 53 of FIG. 8 has a substantially rectangularperimeter and is located at the lower second surface 52 of package 50.Each contact 53 includes a planar or substantially planar upper firstsurface 31, an opposite planar or substantially planar second surface32, three internal side surfaces 33 (only one is shown in FIG. 8) havingreentrant portions, and one external orthogonal side surface 55. Secondsurface 32 of contact 53 is in the same plane as lower second surface 52of package 50.

[0068] First surface 31 and side surfaces 33 of contacts 53 are coveredwith an encapsulant material. Second surface 32 and external sidesurface 55 of contacts 53 are not covered with encapsulant material.

[0069] Orthogonal external side surfaces 55 of contacts 53 of FIG. 8were formed during Step 6 of FIG. 1 when the saw cut the connectionsbetween tabs 30 and members 23 and 23A of leadframe 20 of FIG. 2.Accordingly, the external side surface 55 of each contact 53 has avertical profile which is the same plane as the corresponding verticalside 57 of package 50.

[0070] Although not shown in FIG. 8, the three internal side surfaces 33(only one is shown) of each contact 53 have reentrant portions, asexemplified by FIGS. 3-6. In addition side surfaces 33 may haveasperities, as exemplified by FIGS. 3-5. Both the reentrant portion(s)and asperities of contacts 53 enhance the connection between contacts 53and encapsulant material 40 of package 50 of FIG. 8.

[0071] The perimeter of contacts 53 need not be substantiallyrectangular in shape. For example, if tabs 30 of leadframe 20 of FIG. 2had a circular perimeter, then contacts 53 would have a largely circularperimeter with a rectilinear portion formed during the cutting of tab 30from leadframe 20 in Step 6.

[0072] A bond wire 58 is connected between each bonding pad 56 a of die56 and the upper first surface 31 of each contact 53. Bond wire 58electrically connects individual bonding pads 56 a of die 56 toindividual contacts 53.

[0073] Second surface 32 of contacts 53 of FIG. 8 may be directlyconnected to an external printed circuit board, as in an LCC package.Alternatively, a solder interconnection bump may be formed on contacts53 for physically and electrically connecting package 50 to a printedcircuit board. FIG. 9 shows a solder interconnection bump 60 formed onlower second surface 32 and external side surface 55 of each contact 53of package 50 of FIG. 8.

[0074] In an alternative embodiment, second surface 26 of die pad 24also may be connected, such as by solder paste, to the printed circuitboard to facilitate package cooling. The cooling occurs by thermalconduction.

[0075]FIG. 10 is a flow chart for an alternative assembly method, inaccordance with the present invention, for constructing a package likethat of FIG. 8. In the method of FIG. 10, a plurality of packages areconstructed simultaneously. The basic steps of the FIG. 10 process arethe same as the FIG. 1 process.

[0076] Step 1 of FIG. 10 provides a thin metal leadframe which includesa plurality of interconnected rectangular frames in a matrix. A die padis provided within each frame.

[0077]FIG. 11 shows an exemplary metal leadframe 70, in accordance withthe present invention, suitable for Step 1 of FIG. 10. Shading is usedin FIG. 11 to distinguish metal portions of leadframe 70 from emptyspace between the components of leadframe 70.

[0078] Leadframe 70 of FIG. 11 is planar or substantially planar and isformed of metal. The metals and methods used for constructing leadframe70 are the same as those described above for leadframe 20 of FIG. 2.

[0079] Leadframe 70 of FIG. 11 includes a disposable rectangular outerframe 71. Outer frame 71 consists of four intersecting members, denotedas members 72-75. Member 72 is parallel to member 74, and member 73 isparallel to member 75.

[0080] Within outer frame 71 of FIG. 11 are four interconnectedrectangular frames in a two by two matrix. These frames are formed bythe intersection of three disposable strips 76 and three disposablestrips 77. Each of the four interconnected frames of FIG. 11 has thesame basic features as frame 21 of FIG. 2. Accordingly, the samereference numbers will be used, where applicable, and associateddiscussion will be abbreviated.

[0081] A rectangular die pad 24 is within and connected to each of thefour frames formed by strips 76 and 77 of FIG. 11. As in FIG. 2, eachdie pad 24 of FIG. 11 has four side surfaces 27. Each side surface 27has a reentrant portion(s), such as in the examples of FIGS. 3-6. Sidesurfaces 27 also may include asperities, such as those shown in FIGS.3-5.

[0082] Three parallel strips 76 are within and connected to frame 71 ofFIG. 11. A first strip 76 is adjacent to, parallel to, and connected tomember 72 of frame 71. A second strip 76 is adjacent to, parallel to,and connected to member 74 of frame 71. A third strip 76 is located inthe center of frame 71 between juxtaposed pairs of die pads 24. Eachstrip 76 of FIG. 11 is connected to each of the die pads 24 which areadjacent to that particular strip 76. A disposable mushroom-shapedanchor 29 connects each strip 76 to each adjacent die pad 24. Twodisposable connectors 78 connect member 72 to its adjacent strip 76, andtwo connectors 78 connect member 74 to its adjacent strip 76. The numberand locations of connectors 76 may vary.

[0083] Three parallel strips 77 also are within and connected to frame71 of FIG. 11. One strip 77 is adjacent to, parallel to, and connectedto side members 73 and 75 of frame 71. A disposable connector 78connects members 73 and 75 to their respective adjacent strip 77. Athird strip 77 is located in the center of frame 71 between juxtaposedpairs of die pads 24.

[0084] The intersecting ends of the peripheral strips 76 and 77 of FIG.11 are connected to the inner corners of outer frame 71. A gate 79extends at approximately a 45 degree angle from each of the four innercorners of frame 71 and connects to the interconnected ends ofperipheral strips 76 and 77. Gate 79 is useful for the introduction ofmolding compound into a mold, where molding is the chosen method ofencapsulation.

[0085] Central strip 76 of FIG. 11 intersects central strip 77 at thecenter of leadframe 70. The ends of central strips 76 and 77 intersectthe peripheral strips 77 and 76, respectively.

[0086] In FIG. 11, a plurality of straight, evenly-spaced, finger-like,rectangular tabs 30 extend in sets of five from each strip 77 toward thesides of each of the die pads 24 adjacent that particular strip 77. Tabs30 do not contact die pads 24. The central strip 77 that is betweenjuxtaposed pairs of die pads 24 has mirror-image sets of five tabs 30which extend in opposite directions toward each of the juxtaposed diepads 24. Each tab 30 will ultimately form a contact 53 of package 50 ofFIG. 8.

[0087] Each tab 30 of FIG. 11 has three side surfaces 33 which have areentrant portion(s), such as shown in FIGS. 3-6. Side surfaces 33 oftabs 53 also may include asperities, such as those shown in FIGS. 3-5.The reentrant portions and asperities of side surfaces 33 of tabs 30enhance the connection between encapsulant material 40 and contacts 53(i.e., severed tabs 30) of a completed package 10 of FIG. 8.

[0088] Step 2 of FIG. 10 places and attaches an integrated circuit die56 on upper first surface 25 of each die pad 24 of leadframe 70 of FIG.11, as described above for Step 2 of FIG. 1.

[0089] Referring to FIGS. 8 and 11, Step 3 of FIG. 10 electricallyconnects a conductive metal bond wire 58 between each bonding pad 56 aon each integrated circuit die 56 attached to leadframe 70 and a tab 30.Bond wire 58 is connected to the first surface 31 of each tab 30. Themethods for Step 3 of FIG. 11 are the same as described above for Step 3of FIG. 1.

[0090] Step 4 of FIG. 10 covers each incomplete package of leadframe 70of FIG. 11, including all of the dies 56, with a conventional viscous,adhesive encapsulant material. The methods and materials used for Step 4of FIG. 10 are the same as for Step 4 of FIG. 1, except that theencapsulant material is applied onto all of the incomplete packages 50of leadframe 70 of FIG. 11. The encapsulant material covers the upperfirst surface of leadframe 70, as well as side surfaces 27 and 33 of diepads 24 and tabs 33, respectively. The encapsulant material is thenhardened into a single block which covers all of the incomplete packagesof leadframe 70 of FIG. 11, as well as all or part of the width ofmembers 72-75 of frame 71 of leadframe 70. Again, the lower secondsurface of leadframe 70, including lower surfaces 26 and 32 of die pads24 and tabs 30, respectively, is not covered by encapsulant material,but instead remains exposed.

[0091] Step 5 of FIG. 10 plates the exposed lower surface of leadframe70 of FIG. 11, including lower second surfaces 26 and 32 of die pads 24and tabs 30, respectively, with a conventional plating metal. This stepis accomplished as described above for Step 5 of FIG. 1.

[0092] Step 6 of FIG. 10 cuts leadframe 70 of FIG. 11 after theencapsulation step. Encapsulated leadframe 70 is cut in situ, similar toleadframe 20 of FIG. 7. The disposable portions of leadframe 70 areeither severed from the packages, obliterated, or isolated byencapsulant material from the other components of package 50 of FIG. 8.The requirements of and methods used for Step 6 of FIG. 10 are basicallythe same as described above for Step 6 of FIG. 1, except that more cutshave to be made because leadframe 70 of FIG. 11 is bigger and has morecomponents than leadframe 20 of FIG. 2.

[0093] Step 6 of FIG. 10 severs the connection between tabs 30 andstrips 77 of leadframe 70. This cut forms the isolated, individualcontacts 53 shown in package 50 of FIG. 8. Step 6 also severs theconnection between anchors 29 and strips 76. This cut physicallyisolates die pads 24 within the encapsulant material. Step 6 also cutsthrough the single block of encapsulant material formed during Step 4 toform four packages 50 from leadframe 70 of FIG. 11.

[0094] Step 6 may be performed using a saw or other cutting apparatus.Where a saw is used for Step 6, the saw is moved along strips 76 and 77(See FIG. 11). The saw blade used should be wider than strips 76 and 77of FIG. 11, but narrower than the combined width of central strip 77 andthe back-to-back tabs 30. As a result, moving the saw blade along strips76 and 77 will obliterate strips 76 and 77, but will not obliterate tabs30. As discussed above, the surface, area of tabs 30 must be maintainedbecause the severed tabs 30 become contacts 53 in package 50 of FIG. 8.

[0095] An exemplary method of accomplishing Step 6 of FIG. 10 includes afirst step of inverting the encapsulated leadframe 70 and placing it onsticky paper. Using the exposed portions of leadframe 70 of FIG. 11 as apattern, three parallel cuts are made, each of which goes through sidemembers 73 and 75 and along and through the length of a strip 76 ofleadframe 70. These three cuts form two of the four external sidesurfaces 57 of package 50 of FIG. 8; obliterate strips 76; and sever theconnections between die pads 24 and strips 76.

[0096] Next, the encapsulated leadframe 70 is rotated 90 degrees, andthree parallel cuts are made perpendicular to the original three cuts.Each of these latter three cuts goes through side members 72 and 74 andalong and through the length of a strip 77. These latter three cuts alsoform the remaining two external side surfaces 57 of package 50 of FIG.8. Since the width of the saw blade is selected to be wider than strips76 and 77, but narrower than the combination of central strip 77 andtabs 30, the latter three cuts obliterate strips 77 but do notobliterate the tabs 30 which are attached to strips 77.

[0097] The six cuts described above complete the formation of the fourpackages 50 from leadframe 70 of FIG. 11 by separating the completedpackages from one another and from the disposable portions of leadframe70.

[0098] Artisans will appreciate that numerous variations of thepackages, leadframes, and assembly methods described above are possible.As one example, changes can be made to leadframe 70 of FIG. 11 in orderto change the size, shape and numbers of the packages 50 (FIG. 7) formedfrom leadframe 70. For example, instead of simultaneously forming fourpackages using a leadframe like leadframe 70 of FIG. 11, the size of theleadframe may be adjusted so that two, eight, sixteen, forty-eight orsome other number of packages are formed simultaneously. As anotherexample, one may multiply the number of packages formed simultaneouslyby forming several leadframes 70 adjacent to each other on a singlestrip of rolled stock, and processing all of the leadframes 70 on thestrip simultaneously. As another example, the peripheral shapes of diepads 24 and tabs 30 may be changed from rectangular to some other shape.

[0099] In addition, the profiles of side surfaces 27 and 33 of die pads24 and tabs 30, respectively, can be altered from the embodiments ofFIGS. 3-6, provided that the function of enhancing the connectionbetween encapsulant material 40 and the die pads 24 and contacts 53 ofpackages 50 of FIG. 8 is maintained.

[0100] Leadframe 70 of FIG. 11 may be modified in other ways as well.For example, the peripheral strips 76 and 77 that are adjacent tomembers 72-75, may be omitted. In such a case, the anchors 29 of FIG. 11would be attached to members 72 and 74, and tabs 30 would be attached tomembers 73 and 75 of frame 71 of leadframe 70.

[0101] As a final example, instead of forming a single block ofencapsulant material over all of the dies and incomplete packages ofleadframe 70 of FIG. 11, a mold having individualized cavities forforming a block of encapsulant material above each the fourinterconnected frames and die pads 24 of leadframe 70 may be used. Insuch a case, less encapsulant material would be cut in Step 6 of FIG.10.

[0102] The above description of embodiments of this invention isintended to be illustrative and not limiting. Other embodiments of thisinvention will be obvious to those skilled in the art in view of theabove disclosure.

1. A package for an integrated circuit die comprising: an integratedcircuit die; a plurality of metal contacts adjacent to peripheral sidesof the package; wherein each contact has a substantially planar firstsurface, an opposite substantially planar second surface, and a sidesurface between said first and second surfaces; wherein said firstsurface has a bond wire connected thereto, said second surface isexposed at a first external surface of the package, and said sidesurface includes a reentrant portion; and an encapsulant material whichcovers the integrated circuit die and the reentrant portion of the sidesurface of each contact.
 2. The package of claim 1, further comprising:a die pad having a substantially planar first surface, an oppositesubstantially planar second surface, and a side surface between thefirst surface and the second surface; and wherein the side surface ofthe die pad has a reentrant portion, and the encapsulant material coversthe reentrant portion of the side surface of the die pad.
 3. The packageof claim 2, wherein the second surface of the die pad is exposed at thefirst external surface of the package.
 4. The package of claim 2,wherein the die pad is internal to the package.
 5. The package of claim3, wherein each package has a rectangular perimeter and has fourperipheral sides, and said contacts are aligned in a row along twoopposite peripheral sides of the package.
 6. The package of claim 3,wherein said contacts are aligned in a row along each of the fourperipheral sides of the package.
 7. The package of claim 3, wherein theside surfaces of the die pad and contacts include a central peak.
 8. Thepackage of claim 3, wherein the side surfaces of the die pad andcontacts include a central depression.
 9. The package of claim 3,wherein the side surfaces of the die pad and contacts include a lipadjacent to the first surface of the die pad and contacts, respectively,and a reentrant orthogonal portion adjacent to said lip.
 10. The packageof claim 3, wherein the side surfaces of the die pad and contactsinclude asperities.
 11. A package for an integrated circuit diecomprising: an integrated-circuit die; a plurality of metal contactsadjacent to peripheral sides of the package; wherein each contact has asubstantially planar first surface, an opposite substantially planarsecond surface, and a side surface between said first and secondsurfaces; wherein said first surface has a bond wire connected thereto,said second surface is exposed at a first external surface of thepackage, and said side surface includes a reentrant portion; a die padupon which the integrated circuit die is placed, said die pad includinga peripheral side surface; and an encapsulant material which covers theintegrated circuit die and the side surfaces of each contact and the diepad; and wherein the side surface of each contact includes a means forenhancing the connection between the encapsulant material and thecontact, and the side surface of the die pad includes a means forenhancing the connection between the encapsulant material and the diepad.
 12. A leadframe for making an encapsulated integrated circuit diepackage comprising: a frames; a die pad within and connected to theframe, wherein said die pad has a side surface; a plurality ofsubstantially planar tabs which extend from the frame toward the die padwithout contacting the die pad, wherein each tab includes a sidesurface; and wherein the side surfaces of the die pad and tabs include areentrant portion.
 13. The leadframe of claim 12, wherein the sidesurfaces of the die pad and tabs include a central peak.
 14. Theleadframe of claim 12, wherein the side surfaces of the die pad and tabsinclude a central depression.
 15. The leadframe of claim 12, wherein thedie pad and tabs have a first surface, and the side surfaces of the diepad and tabs include a lip adjacent to the first surface, and areentrant orthogonal portion adjacent to said lip.
 16. The leadframe ofclaim 12, wherein the side surfaces of the die pad and contacts includeasperities.
 17. A leadframe for making a plurality of encapsulatedintegrated circuit die packages comprising: a plurality of die pads,wherein each die pad has a side surface; a plurality of interconnectedframes in a matrix, wherein one of said die pads is within and connectedto each of the frames; and a plurality of substantially planar tabswhich extend from each frame toward the die pad within the particularframe without contacting the die pad; and wherein the side surfaces ofthe die pads and tabs include a reentrant portion.
 18. The leadframe ofclaim 17, wherein the side surfaces of the die pads and tabs include acentral peak.
 19. The leadframe of claim 17, wherein the side surfacesof the die pads and tabs include a central depression.
 20. The leadframeof claim 17, wherein the die pads and tabs have a first surface, and theside surfaces of the die pads and tabs include a lip adjacent to saidfirst surface, and a reentrant orthogonal portion adjacent to said lip.21. The leadframe of claim 17, wherein the side surfaces of the die padsand contacts include asperities.
 22. A method of making an integratedcircuit die package comprising: providing a substantially planar metalleadframe, said leadframe including a frame; wherein a substantiallyplanar die pad is within and connected to the frame, and substantiallyplanar tabs extend from the frame toward the die pad without contactingthe die pad; and wherein the die pad and tabs each have a first surface,an opposite second surface, and a side surface, and the side surfaces ofthe die pad and tabs include a reentrant portion; placing an integratedcircuit die on the first surface of die pad; electrically connecting theintegrated circuit die to the first surface of the tabs; applying anencapsulant material onto the frame so that the integrated circuit die,the first surfaces of the die pad and tabs, and the side surfaces of thedie pad and tabs are covered with the encapsulant material, but thesecond surfaces of the tabs are not covered; hardening the encapsulantmaterial; and cutting the encapsulated frame so that the die pad andtabs are severed from the frame, a completed package including a die, adie pad, and severed tabs is detached from the leadframe, and saidsevered tabs are adjacent to peripheral sides of the package.
 23. Themethod of claim 22, wherein the second surface of the die pad also isnot covered with encapsulant material.
 24. The method of claim 23,further including cutting encapsulant material to form the peripheralsides of the package.
 25. The method of claim 24, wherein the cutting isdone by sawing.
 26. The method of claim 23, further comprising platingthe second surfaces of the die pad and tabs with a metal after applyingthe encapsulant material.
 27. The method of claim 22, further comprisingconnecting the leadframe to electrical ground.
 28. A method of making aplurality of integrated circuit packages comprising: providing asubstantially planar metal leadframe, said leadframe including aplurality of interconnected frames in a matrix; wherein a substantiallyplanar die pad is within and connected to each of the frames; wherein aplurality of substantially planar tabs extend from each frame toward thedie pad within the frame without contacting the die pad; wherein the diepads and tabs each have first surface, an opposite second surface, and aperipheral side surface; and wherein the side surfaces of the die padsand tabs include a reentrant portion; placing an integrated circuit dieon the first surface of each die pad; electrically connecting eachintegrated circuit die to the first surface of the tabs which extendtoward the particular die; applying an encapsulant material onto each ofthe frames so that the integrated circuit dies, the first surfaces ofthe die pads and the tabs, and the side surfaces of the die pads andtabs are covered with the encapsulant material, but the second surfacesof the tabs are not covered; hardening the encapsulant material; andcutting the encapsulated frames so that the die pads and tabs aresevered from their respective frames, a plurality of completed packageseach including a die, a die pad, and severed tabs are formed, and thesecond surfaces of the severed tabs of each package are adjacent toperipheral sides of the package.
 29. The method of claim 28, wherein thesecond surface of the die pad also is not covered with encapsulantmaterial.
 30. The method of claim 29, wherein the cutting is done withby sawing.
 31. The method of claim 29, further comprising plating thesecond surfaces of the die pads and tabs with a metal after applying theencapsulant material.
 32. The method of claim 28, wherein a single blockof encapsulant material covers all of the dies, and furtherincluding-cutting encapsulant material to form the peripheral sides ofthe packages.
 33. The method of claim 28, wherein each die is within aseparate unit of encapsulant material.
 34. The method of claim 28,further comprising connecting the leadframe to electrical ground.
 35. Amethod of making a leadframe comprising: chemically etching a metalsheet to form a frame; wherein a die pad is within and connected to theframe, tabs extend from the frame toward the die pad without contactingthe die pad, and the die pad and tabs each have a peripheral sidesurface which includes a reentrant portion.
 36. A method of making aleadframe comprising: progressively stamping a metal sheet to form aframe; wherein a die pad is within and connected to the frame, tabsextend from the frame toward the die pad without contacting the die pad,and the die pad and tabs each have a peripheral side surface whichincludes a reentrant portion.